[Intel-gfx] [PATCH 1/3] drm/i915: Displayport compliance test 4.2.2.9 support

[Todd Previte]

Implement the fix for test 4.2.2.9. This test is a 4-block E-DDC
read over the AUX channel. For test purposes, the normal 1-block
EDID read is required to write the checksum of that block to the
sink device via the AUX channel. For 4.2.2.9, that checksum must
be the checksum of the last block read. The DRM EDID read code
already does the 4-block read, so the checksum just needs to be
adjusted to the one that we need based on the number of extensions
detected in the block.

Signed-off-by: Todd Previte <tprevite at gmail.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index c7cbb67..14147d0 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4020,9 +4020,17 @@ static uint8_t intel_dp_autotest_edid(struct intel_dp *intel_dp)
 				      intel_dp->aux.i2c_defer_count);
 		intel_dp->compliance_test_data = INTEL_DP_RESOLUTION_FAILSAFE;
 	} else {
+		/* Checksum write for EDID reads (DP CTS 1.2 Core r1.1)
+		 *    4.2.2.3: checksum of EDID block 0
+		 *    4.2.2.9: checksum of the last 128-byte block read
+		 */
+		int checksum = *(&intel_connector->detect_edid->checksum +
+				 (intel_connector->detect_edid->extensions *
+				  EDID_LENGTH));
+
 		if (!drm_dp_dpcd_write(&intel_dp->aux,
 					DP_TEST_EDID_CHECKSUM,
-					&intel_connector->detect_edid->checksum,
+					&checksum,
 					1))
 			DRM_DEBUG_KMS("Failed to write EDID checksum\n");
 
-- 
1.9.1